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Four p38 MAPK isoforms (alpha, beta, gamma and delta respectively) have been identified, each displaying different patterns of tissue expression. The p38 MAPK alpha and beta isoforms are found ubiquitously throughout the body; are present in many different cell types and are inhibited by a number of previously described small molecular weight compounds. Early classes of inhibitors were highly toxic due to the broad tissue distribution of these isoforms which resulted in off-target effects of the compounds. Some of the more recently identified inhibitors show improved selectivity for p38 MAPK alpha and beta isoforms and have wider safety margins.
p38 MAP kinase is believed to play a pivotal role in many of the signalling pathways that are involved in initiating and maintaining chronic, persistent inflammation in human disease, for example, in severe asthma, COPD and inflammatory bowel disease (IBD). There is now an abundant literature which demonstrates that p38 MAP kinase is activated by a range of pro-inflammatory cytokines and that its activation results in the recruitment and release of further pro-inflammatory cytokines. Indeed, data from some clinical studies demonstrate beneficial changes in disease activity in patients during treatment with p38 MAP kinase inhibitors. For instance Smith describes the inhibitory effect of p38 MAP kinase inhibitors on TNFα (but not IL-8) release from human PBMCs (Smith, S. J., Br. J. Pharmacol., 2006, 149:393-404).
The use of inhibitors of p38 MAP kinase in the treatment of COPD and IBD has also been proposed. Small molecule inhibitors targeted to p38 MAPKα/β have proved to be effective in reducing various parameters of inflammation in:                cells and tissues obtained from patients with COPD, who are generally corticosteroid insensitive (Smith, S. J., Br. J. Pharmacol., 2006, 149:393-404);        biopsies from IBD patients (Docena, G. et al., J. of Trans. Immuno/., 2010, 162:108-115); and        in vivo animal models (Underwood, D. C. et al., Am. J. Physiol., 2000, 279:L895-902; Nath, P. et al., Eur. J. Pharmacol., 2006, 544:160-167).        
Irusen and colleagues also suggested the possibility of involvement of p38 MAPKα/β on corticosteroid insensitivity via the reduction of binding affinity of the glucocorticoid receptor (GR) in nuclei (Irusen, E. et al., J. Allergy Clin. Immunol., 2002, 109:649-657). Clinical investigations in inflammatory diseases with a range of p38 MAP kinase inhibitors, including AMG548, BIRB 796, VX702, SCIO469 and SCIO323, has been described (Lee, M. R. and Dominguez, C., Current Med. Chem., 2005, 12:2979-2994). However, the major obstacle hindering the utility of p38 MAP kinase inhibitors in the treatment of human chronic inflammatory diseases has been the toxicity observed in patients. This has been sufficiently severe to result in the withdrawal from clinical development of many of the compounds progressed, including all those specifically mentioned above.
COPD is a condition in which the underlying inflammation is reported to be substantially resistant to the anti-inflammatory effects of inhaled corticosteroids. Consequently, a superior strategy for treating COPD would be to develop an intervention which has both inherent anti-inflammatory effects and the ability to increase the sensitivity of the lung tissues of COPD patients to inhaled corticosteroids. The recent publication of Mercado et al. (2007; American Thoracic Society Abstract A56) demonstrates that silencing p38 MAPK γ has the potential to restore sensitivity to corticosteroids. Thus, there may be a dual benefit for patients in the use of a p38 MAP kinase inhibitor for the treatment of COPD.
Many patients diagnosed with asthma or with COPD continue to suffer from uncontrolled symptoms and from exacerbations of their medical condition that can result in hospitalisation. This occurs despite the use of the most advanced, currently available treatment regimens, comprising of combination products of an inhaled corticosteroid and a long acting β-agonist. Data accumulated over the last decade indicates that a failure to manage effectively the underlying inflammatory component of the disease in the lung is the most likely reason that exacerbations occur. Given the established efficacy of corticosteroids as anti-inflammatory agents and, in particular, of inhaled corticosteroids in the treatment of asthma, these findings have provoked intense investigation. Resulting studies have identified that some environmental insults invoke corticosteroid-insensitive inflammatory changes in patients' lungs. An example is the response arising from virally-mediated upper respiratory tract infections (URTI), which have particular significance in increasing morbidity associated with asthma and COPD.
It has been disclosed previously that compounds that inhibit the activity of both the c-Src and Syk kinases are effective agents against rhinovirus replication (Charron, C. E. et al., WO 2011/158042) and that compounds that inhibit p59-HCK are effective against influenza virus replication (Charron, C. E. et al., WO 2011/070369). Taken together with inhibition of p38 MAPK, these are particularly attractive properties for compounds to possess that are intended to treat patients with chronic respiratory diseases.
Certain p38 MAPK inhibitors have also been described as inhibitors of replication of respiratory syncitial virus (Cass L. et al., WO 2011/158039).
The precise etiology of IBD is uncertain, but is believed to be governed by genetic and environmental factors that interact to promote an excessive and poorly controlled mucosal inflammatory response directed against components of the luminal microflora. This response is mediated through infiltration of inflammatory neutrophils, dendritic cells and T-cells from the periphery. Due to the ubiquitous expression of p38 in inflammatory cells it has become an obvious target for investigation in IBD models. Studies investigating the efficacy of p38 inhibitors in animal models of IBD and human biopsies from IBD patients indicated that p38 could be a target for the treatment of IBD (Hove, T. ten et al., Gut, 2002, 50:507-512, Docena, G. et al., J. of Trans. Immunol., 2010, 162:108-115). However, these findings are not completely consistent with other groups reporting no effect with p38 inhibitors (Malamut G. et al., Dig. Dis. Sci, 2006, 51:1443-1453). A clinical study in Crohn's patients using the p38 alpha inhibitor BIRB796 demonstrated potential clinical benefit with an improvement in C-reactive protein levels. However this improvement was transient, returning to baseline by week 8 (Schreiber, S. et al., Clin. Gastro. Hepatology, 2006, 4:325-334). A small clinical study investigating the efficacy of CNI-1493, a P38 and Jnk inhibitor, in patients with severe Crohn's disease showed significant improvement in clinical score over 8 weeks (Hommes, D. et al. Gastroenterology. 2002 122:7-14).
T cells are known to play key role in mediating inflammation of the gastrointestinal tract. Pioneering work by Powrie and colleagues demonstrated that transfer of naive CD4+ cells into severly compromised immunodeficient (SCID) animals results in the development of colitis which is dependent on the presence of commensal bacteria (Powrie F. et al. Int Immunol. 1993 5:1461-71). Furthermore, investigation of mucosal membranes from IBD patients showed an upregulation of CD4+ cells which were either Th1 (IFNg/IL-2) or Th2 (IL5/TGFb) biased depending on whether the patient had Crohn's disease or ulcerative colitis (Fuss I J. et al. J Immunol. 1996 157:1261-70). Similarly, T cells are known to play a key role in inflammatory disorders of the eye with several studies reporting increased levels of T cell associated cytokines (IL-17 and IL-23) in sera of Bechets patients (Chi W. et al. Invest Ophthalmol Vis Sci. 2008 49:3058-64). In support, Direskeneli and colleagues demonstrated that Behcets patients have increased Th17 cells and decreased Treg cells in their peripheral blood (Direskeneli H. et al. J Allergy Clin Immunol. 2011 128:665-6).
One approach to inhibit T cell activation is to target kinases which are involved in activation of the T cell receptor signalling complex. Syk and Src family kinases are known to play a key role in this pathway, where Src family kinases, Fyn and Lck, are the first signalling molecules to be activated downstream of the T cell receptor (Barber E K. et al. PNAS 1989 86:3277-81). They initiate the tyrosine phosphorylation of the T cell receptor leading to the recruitment of the Syk family kinase, ZAP-70. Animal studies have shown that ZAP-70 knockout results in a SCID phenotype (Chan A C. et al. Science. 1994 10; 264(5165):1599-601).
A clinical trial in rheumatoid arthritis patients with the Syk inhibitor Fostamatinib demonstrated the potential of Syk as an anti-inflammatory target with patients showing improved clinical outcome and reduced serum levels of IL-6 and MMP-3 (Weinblatt M E. et al. Arthritis Rheum. 2008 58:3309-18). Syk kinase is widely expressed in cells of the hematopoietic system, most notably in B cells and mature T cells. Through interaction with immunoreceptor tyrosine-based activation (ITAM) motifs it plays an important role in regulating T cell and B cell expansion as well as mediating immune-receptor signalling in inflammatory cells. Syk activation leads to IL-6 and MMP release inflammatory mediators commonly found upregulated in inflammatory disorders including IBD and rheumatoid arthritis (Wang Y D. et at World I Gastroenterol 2007; 13: 5926-5932, Litinsky I et al. Cytokine. 2006 January 33:106-10).
In addition to playing key roles in cell signalling events which control the activity of pro-inflammatory pathways, kinase enzymes are now also recognised to regulate the activity of a range of cellular functions, including the maintenance of DNA integrity (Shilo, Y. Nature Reviews Cancer, 2003, 3: 155-168) and co-ordination of the complex processes of cell division. Indeed, certain kinase inhibitors (the so-called “Olaharsky kinases”) have been found to alter the frequency of micronucleus formation in vitro (Olaharsky, A. J. et al., PLoS Comput. Biol., 2009, 5(7)). Micronucleus formation is implicated in, or associated with, disruption of mitotic processes and is therefore undesirable. Inhibition of glycogen synthase kinase 3α (GSK3α) was found to be a particularly significant factor that increases the likelihood of a kinase inhibitor promoting micronucleus formation. Also, inhibition of the kinase GSK3β with RNAi has been reported to promote micronucleus formation (Tighe, A. et al., BMC Cell Biology, 2007, 8:34).
Whilst it may be possible to attenuate the adverse effects of inhibition of Olaharsky kinases such as GSK3α by optimisation of the dose and/or by changing the route of administration of a molecule, it would be advantageous to identify further therapeutically useful molecules with low or negligible inhibition of Olaharsky kinases, such as GSK 3α and/or have low or negligible disruption of mitotic processes (e.g. as measured in a mitosis assay).
Various urea derivatives are disclosed as having anti-inflammatory properties (see, for example, WO 01/36403, WO 01/4115, WO 02/092576, WO 2003/068228, WO 2003/072569, WO 2004/113352, WO 2007/053394 and Bioorg. Med. Chem. Lett. 2007, 17, 354-357). Nevertheless, there remains a need to identify and develop alternative p38 MAP kinase inhibitors, and particularly inhibitors that have improved therapeutic potential over currently available treatments or, in particular, that exhibit a superior therapeutic index (e.g. inhibitors that are at least equally efficacious and, in one or more respects, are less toxic at the relevant therapeutic dose than previous agents).